Rail passengers are facing higher fares across the UK as average price increases of 2.3% are introduced on the first weekday of the new year.

The increase covers regulated fares, including season tickets, and unregulated, such as off-peak tickets.

Campaigners said the rise was a "kick in the teeth" for passengers after months of widespread strike disruption.

The government said it was delivering the biggest rail modernisation programme for more than a century.

The increase in fares came as a strike by conductors on Southern Rail entered its third day, as a long-running row about the role of guards on new trains continued.

The RMT union began the 72-hour walkout on New Year's Eve, while another strike is set for 9 January.

Why are prices rising?

Image copyrightDan Kitwood

By Richard Westcott, BBC transport correspondent

Even if you allow for inflation, rail fares have gone up by around 25% since the mid-1990s.

Some tickets have spiked by 40% in just a decade.

Why? Because successive governments have been changing the proportion of the rail bill paid for by passengers.

It used to be around 50%. Today it's around 70%.

It does of course mean that other taxpayers, who do not catch trains (and that's most people, frankly), are paying less to run them.

Ironically, the original idea behind the government regulating around half of our rail fares was to protect passengers from big price rises imposed by train operators.

Yet it's often been government ministers who have used the mechanism to put fares up.

Bruce Williamson, of the independent campaign group Railfuture, said: "With the chaos on Southern, lacklustre performance in Scotland and stalled electrification on the Great Western main line, passengers are going to wonder what they are getting for their increased ticket price."

Lianna Etkind, of the Campaign for Better Transport, said: "Today's fare rises are another kick in the teeth for long-suffering rail passengers.

"Many experienced a less frequent and more overcrowded service last year, and now they are required to pay more for the same this year."

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Media captionRail Delivery Group chief tells Radio 4's Today increase in fares is needed due to railway's "success"

The government uses the previous July's Retail Prices Index (RPI) measure of inflation to determine increases in regulated train fares, which was 1.9%.

Train operating companies set the prices of other tickets but are bound by competition rules.

New trains

According to the Rail Delivery Group (RDG), which represents train operators, around 97p in every pound paid by passengers goes back into running and improving services.

RDG chief executive Paul Plummer said: "Nobody wants to pay more to travel to work and at the moment in some places people aren't getting the service they are paying for.

"However, increases to season tickets are set by government. Money from fares is helping to sustain investment in the longer, newer trains and more punctual journeys that passengers want."

Transport Secretary Chris Grayling said the government has "always fairly balanced" the cost of modernising the railways between the taxpayer and the passenger."

But shadow transport secretary Andy McDonald said passengers are always told that higher fares are necessary to fund investment.

"The truth is that our heavily fragmented railways mean that it takes years longer and costs much more than it should to deliver basic improvements," he said.